Detergent compositions for body use generally contain anionic surfactants, such as an N-alkylacylamino acid-based surfactant, as the main component. For example, JP-A-63-2962 discloses a liquid detergent composition in which an N-alkylacylamino acid-based surfactant is used as a low irritative base material. (The term "JP-A" as used herein means an "unexamined published Japanese patent application".)
However, the N-alkylacylamino acid surfactants contained in the prior art detergents are tertiary amide type N-alkyl-N-acylamino acid salts, and they give an unpleasant feeling when used, such as poor foam breakage, a slimy feel and the like, though they have excellent water solubility.
In addition, JP-A-63-2962 discloses at its Example 5 N-lauroyl-.beta.-alanine sodium salt which is a secondary amide type N-acylamino acid salt. This salt, however, is hardly applicable to a liquid detergent because of its low water solubility. Also, JP-A-63-2962 further discloses to employ the compound at a concentration of 1%, but the compound could not give an excellent feeling upon use even when it was employed in such concentration.
In consequence, great concern has been directed toward the development of a liquid detergent composition which is hardly irritative against the skin and hair, has high detergency and gives an excellent feeling upon use.
On the other hand, the present inventors have found as a result of intensive investigation that an N-acylated amino acid salt which is used in the present invention as component (A) can provide a hardly irritative detergent composition having high detergency and excellent feeling upon use. However, when such an N-acylated amino acid salt is employed in a liquid detergent having a pH value ranging from 6 to 8, it gives precipitation of crystals of an N-acrylated amino acid, which is an unneutralized compound of the N-acrylated amino acid salt, so that a stable liquid detergent composition has hardly been obtained with the use of the N-acrylated amino acid salt.